The Orbit and Distance of WR140 - Proceedings of "Stellar Winds in Interaction" 2010

TL;DR

This study uses multi-epoch VLBA and IR interferometry to analyze the orbit, orientation, and distance of the WR140 colliding-wind binary system, providing detailed orbital parameters and a new distance estimate.

Contribution

The paper presents the first combined VLBA and IR interferometry analysis to determine the orbit and distance of WR140 with high precision.

Findings

Orbit inclination: 120°±4°

Distance to WR140: 1.81±0.08 kpc

Orbit semimajor axis: 9.0±0.1 mas

Abstract

A campaign of 35 epochs of milli-arcsec resolution VLBA observations of the archetype collidingwind WR+O star binary system WR140 show the wind-collision region (WCR) as a bow-shaped arc of emission that rotates as the highly eccentric orbit progresses. The observations comprise 21 epochs from the 1993- 2001 orbit, discussed by Dougherty et al. (2005), and 14 epochs from the 2001-2009 orbit, and span orbital phase 0.43 to 0.95. Assuming the WCR is symmetric about the line-of-centres of the two stars and "points" at the WR star, this rotation shows the O star moving from SE to E of the WR star between these orbital phases. Using IR interferometry observations from IOTA that resolve both stellar components at phase 0.297 in conjunction with orbital parameters derived from radial velocity variations, the VLBA observations constrain the inclination of the orbit plane as 120{\deg}\pm4{\deg}, the longitude of the ascending node as 352{\deg}\pm2{\deg}, and the orbit semimajor axis as 9.0\pm0.1 mas. This leads to a distance estimate to WR140 of 1.81\pm0.08 kpc. Further refinements of the orbit and distance await more IR interferometric observations of the stellar components directly.